Heart failure (HF) is a debilitating disease with poor prognosis. Excess signaling through cardiac G-protein G?? subunits is an important component of HF pathophysiology. They recruit elevated levels of cytosolic G-protein coupled receptor kinase 2 (GRK2, bARK1) to agonist-stimulated b-ARs in HF, leading to the chronic b-AR desensitization and down-regulation that are hallmarks of HF. Previous data has suggested that inhibiting G?? signaling and its interaction with GRK2 could be of therapeutic value in HF. We recently developed a novel small molecule targeting strategy to selectively inhibit G?? binding interactions, and identified several G?? small molecule inhibitors (Bonacci et al, Science, 2006). In particular, compounds M119 and gallein, essentially identical in both structure and function, were found to block G?? -GRK2 interaction in vitro. Our preliminary data further demonstrate that they reduce GRK2 membrane recruitment, enhanced adenylyl cyclase activity, and increased contractility in isolated adult cardiomyocytes in response to b-AR agonist. In vivo, systemic delivery normalized cardiac function, morphology and GRK2 expression in an acute pharmacologic HF model. Importantly, daily treatment for one month halted the progression of HF and pathologic cardiac remodeling when administered to mice with established HF. Recent data demonstrates that elevated adrenal G?? -GRK2 signaling in HF leads to desensitization of adrenal a2-AR feedback inhibition of adrenal catecholamine release. These data suggest that simultaneous inhibition of both cardiac and adrenal G?? -GRK2 signaling could be of substantial therapeutic benefit in HF. Pathologic cardiac G?? signaling was recently found to interact with and result in novel, sustained ERK1/2 phosphorylation at T188; this sustained phosphorylation event has been directly associated with HF. Finally, G?? also signals to PI3K?, the only G?? - regulated PI3K. Large peptide disruption of either PI3K? activity or of PI3K? interaction with GRK2 and their recruitment to G?? is also known to normalize 2-AR signaling and cardiac function in HF models. We have now identified specific G?? inhibitory compounds that block G?? interaction with GRK2, PI3K?, or both. Our overall hypothesis is that selective small molecule targeting of G?? in the heart and in the adrenal gland is a novel therapeutic paradigm for HF, and that general and selective G?? compounds will enhance our current understanding of pathologic G?? signaling in the heart. To address this hypothesis, we propose the following specific aims: 1) Determine the efficacy and cardiac specificity of small molecule G?? inhibition in surgical models of HF. 2) Determine the adrenal role of small molecule G?? inhibition in HF. 3) Determine the role of G?? interaction with a novel ERK1/2 pathway, GRK2 or PI3K? in pathologic cardiac signaling, hypertrophy and cardiomyocyte contractility. In summary, we have exciting preliminary data identifying selective, bioavailable G?? inhibitory compounds that both prevent HF and halt HF progression. Experiments outlined in this proposal may provide a novel therapeutic strategy for HF.